Issue 8, 2005

Contribution of the intramolecular hydrogen bond to the shift of the pKa value and the oxidation potential of phenols and phenolate anions

Abstract

Intramolecularly OH⋯O[double bond, length as m-dash]C hydrogen bonded phenols, 2-HO–C6H2-3,5-(t-Bu)2–CONH–t–Bu (1OH), 2-HO–C6H2-5-t-Bu-1,3-(CONH-t-Bu)2 (2OH) and 2-HO–C6H2-3,5-(t-Bu)2–NHCO–t–Bu (4OH), were synthesized and their phenolate anions were prepared as tetraethylammonium salts (1O(NEt4+), 2O(NEt4+) and 4O(NEt4+)) with intramolecular NH⋯O(oxyanion) hydrogen bonds. 4-HO–C6H2-3,5-t-Bu2–CONH–t–Bu (3OH) and its phenolate anion, 3O(NEt4+), were synthesized as non-hydrogen bonded references. The presence of intramolecular hydrogen bonds was established through the crystallographic analysis and/or 1H NMR spectroscopic results. Intramolecular NH⋯O(phenol) hydrogen bonds shift the pKa of the phenol to a more acidic value. The results of cyclic voltammetry show that the intramolecular OH⋯O[double bond, length as m-dash]C hydrogen bond negatively shifts the oxidation potential of the phenol. In contrast, the intramolecular NH⋯O(oxyanion) hydrogen bond positively shifts the oxidation potential of the phenolate anion, preventing oxidation. These contributions of the hydrogen bond to the pKa value and the oxidation potentials probably play an important role in the formation of a tyrosyl radical in photosystem II.

Graphical abstract: Contribution of the intramolecular hydrogen bond to the shift of the pKa value and the oxidation potential of phenols and phenolate anions

Supplementary files

Article information

Article type
Paper
Submitted
04 Jan 2005
Accepted
23 Feb 2005
First published
10 Mar 2005

Org. Biomol. Chem., 2005,3, 1453-1459

Contribution of the intramolecular hydrogen bond to the shift of the pKa value and the oxidation potential of phenols and phenolate anions

D. Kanamori, A. Furukawa, T. Okamura, H. Yamamoto and N. Ueyama, Org. Biomol. Chem., 2005, 3, 1453 DOI: 10.1039/B419361J

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